1. Field of the Invention
This invention relates to pumps and more particularly to a pump leak monitor for use with a peristaltic pump.
2. Description of the Related Art
Peristaltic pumps have been devised to provide a steady flow of fluid through a conduit by pinching or squeezing the conduit along its length. Various types of peristaltic pumps are used in a wide variety of applications.
In one common form, a peristaltic pump includes a flexible tube that is housed in a circular, usually cylindrical, cavity. The tube is bent such that it extends along the curved inner wall of the cavity and forms a partial loop, hairpin or horseshoe shape. A rotating cam is provided at the center of the cavity for controlling the pump. The cam typically comprises three rollers, spaced 120 degrees apart, that are mounted on a motor-driven rotating carrier. As the rollers move in a circular path, the rollers compress the tube against the inner wall, thereby pinching the tube and pushing the fluid through the tube ahead of the rollers. Accordingly, the peristaltic pump essentially operates as a positive displacement pump wherein each roller pumps the entire volume of the fluid contained in the segment of the tube segment between it and the next roller.
Although peristaltic pumps have gained widespread popularity, the effectiveness of peristaltic pumps is severely limited by the design life of the tube. Due to the compression and relaxation produced by each pass of a roller, the tube in a peristaltic pump is subjected to continual cycles of stresses and strains. Furthermore, the movement of the rollers over the tube creates friction that can abrade the surface of the tube. Over time, the cycles of stretching, compression and abrasion will inevitably cause the tube to rupture. Alternatively, if a line downstream of the pump becomes constricted or occluded, the pressure within the tube can build up to the point wherein a “blowout” occurs. In either case, it is typically very difficult or impossible to predict when the tube will rupture.
Furthermore, in many pump applications, there is no immediate indication that the tube has ruptured within the peristaltic pump. This problem is compounded by the fact that many peristaltic pumps are configured such that it is difficult or impossible to see the condition of the tube during operation. In addition, the peristaltic pump may be located on a rooftop or other remote location. As a result, a ruptured tube may go unnoticed for an extended period of time.
If a tube cracks or ruptures during operation of the pump, fluid will leak from the tube into the pump cavity. As the leaking fluid comes into contact with the pump components, the pump may become irreparably damaged. When the pump is used to move a corrosive chemical, such as chlorine, leakage of the fluid into internal components is particularly harmful. Furthermore, if the problem goes unnoticed, the pump will continue to operate at a reduced level of functionality or may cease to function altogether over an extended period. When the pump is used for a critical function, such as, for example, the treatment of drinking water, biocide feed, or as part of an extracorporeal life support system, the reduced functionality of the pump may have particularly harmful consequences.
In an effort to address this problem, a variety of schemes have been proposed over the years for detecting leaks in peristaltic pumps and other similar devices. However, none of the proposed schemes has met with great commercial success. One reason for the lack of success is the inability of the leakage detection schemes to differentiate between different types of fluids. Many of the existing leakage detection schemes are triggered by the presence of any type of fluid and therefore may provide a false indication of a leak when the pump merely contains condensation, rain water or the like. When a pump contains a relatively innocuous fluid, such as water, and the pump is functioning adequately, it may not be desirable to provide an indication of a leak. Furthermore, when a leak is falsely indicated, much time and effort can be wasted looking for or replacing a broken tube when in fact none exists.
Accordingly, a need exists for an improved pump leak monitor that can quickly and reliably detect the presence of a fluid in a pump cavity. It is desirable that such a pump leak monitor has the capability to differentiate between different types of fluid in the pump cavity. It is also desirable that such a pump leak monitor be capable of use with a peristaltic pump to detect when a harmful fluid has leaked into the pump cavity. It is also desirable that such a pump leak monitor be capable of interconnection to a network for providing a remote indication of pump status. It is also desirable that such a pump leak monitor be quick and reliable and adaptable for use with existing technology.